1. Field of the Invention
The invention relates to a process for producing multilayer material for plain bearings comprising a steel backing and a bronze layer, on which a lead- or tin-based binary layer and a molybdenum-based running-layer are deposited in succession by electroplating. The invention also relates to an electroplating bath for carrying out this process.
2. Description of the Related Art
The development of ever more powerful engines also increases the demands made of the bearings installed in these engines with regard to sustained load carrying capacity, wear resistance and corrosion protection.
Since a particularly significant aspect as far as these bearings are concerned is the improvement of conformation layers, which have to withstand an extremely high surface pressure, plain bearings have been developed which comprise a molybdenum-based running-in layer.
A sliding element is known from DE 29 26 708 A1, on the overlay of which there is provided a molybdenum oxide layer, which has a uniform, micro-flawed structure and is from 0.0005 to 0.003 mm thick. This molybdenum oxide layer is applied to a ternary overlay of PbSn10Cu2, for example. These known plain bearings are distinguished by low wear and enhanced corrosion resistance. However, these materials are not satisfactory if relatively high running speed stability and improved running-in behaviour are required.
Tests with binary overlays, such as PbCu3 for example, which fulfil these requirements somewhat better, have shown, however, that adhesion of the molybdenum oxide layer is unsatisfactory. It became evident that using conventional electrolytes resulted in streaked deposition of the PbCu layer after only a few production batches or a short service life. Light and dark areas were noted, the adhesion of the molybdenum oxide layer being extremely poor in the light areas. In contrast, adhesion in the dark areas of the binary layer was excellent. Furthermore, fluctuations in layer thickness of 12 .mu.m or more were evident, which is unacceptable in the case of highly loadable bearings.